Printing process



Jan. 22, 1946. E. JAHODA ET AL 2,393,378

PRINTING PROCESS Filed Oct! 30, 1944 l4 Wnzn Snow M0151- Fcci- Pub-HINVENTORS Patented Jan. 22, 1946 PRINTING rnocnss Edward Jahofla,Detroit, and c n Witteiunyer,

Mount Fuchs. Detroit, Mich. Application October 30, 1944, Serial No.560,950 1 Claim. (6]. 101-1493) This application relates to the art ofprintin using the ferrogelatin printing process.

In that process, an original whose image lines ing this way,

contain a, primary chemical, such as potassium dichromate, is caused toengage a moist ferrogelatin coated "plate, the coating being sensitizedby the inclusion herein of a secondary chemical,

such as ferrous sulphate. The contact of the Siemens, Mich assignors toWalter M.

ing surface. This way of maintaining water balance is extremelyeffective and desirable. Us-

it is unnecessary to control the in which the printing is humidity ofthe room to wet the printing being done, nor is it necessary surfacefrom the front, and run the risk of emuloriginal image with theferrogelatin coating causes the engaged portions of the ferrogelatincoating to be chemically affected superficially,

that is, only on the surface, to'form, against the unaffected parts ofthe ferrogelatin coating, which remain soft or unhardened, a superficialimage whose lines are oxidized or dulled or hardened. The hardeningwhich forms 'the image is merely superficial, but is sumcient to have agreater amnity for greasy printers ink than the background which, whensuiliciently so It is known that, in printing with a ferrogelatin moist,has no such amnity.

coated plate so affected by an original image, hereafter known as aprintingplate, it is desirproviding, 10

, sifying the ink.

The present invention maybe practiced by as the printing plate, a thinsheet of water absorbent wet strength paper, coated with gelatin andlaid down on 'a wet felt pad. The paper sheet provides an economical,

renewable, inexpensive to discard, stable, printing plate, which is notonly superior to presently known plates because itmay be wetted from theback, but in addition, can be renewed quickly, inexpensively, and veryconvenientlmafter its gelatin coating has had its effectivenessdestroyed by the chemical changes which have taken place in it duringthe printing operation.

A printing plate developed for practicing the invention hereof isdisclosed'diagrammatically in able to keep the gelatin coating surfacemoist,

that is, to maintain what is technically called a -water balance" forsuch surface.

One way of maintaining such water balance is to provide a highfhumidityfor the room. This has obvious disadvantages, but is an acceptedpractice.

Another way or maintaining water balance, is

to apply water to the printing surface by spraying or otherwise wettingit directly. This is not desirable, because ithas been discovered that Iwhen water is applied directly to the printing surface, it has atendency to spread unevenly,

and also to emulsify with the ink.

A third way is to load the gelatin with .a hygroscopic material such asglycerine. This. is also undesirable since glycerine coated materialsare difficult to handle and store.

In commercial practice, particularly where thick gelatin coating'sarespread on a supporting table in a humid room, it is common practice toscrape off or otherwise remove the gelatin coatcoatings. This-hasobvious disadvantages but it the appended drawing.

The plate shown comprises a.v sheet IU of water absorbent, dimensionretaining, wet strength paper, coated on its upper surface with gelatin,and disposed'upon 'a thick-wet felt pad II in turn supported on a tabletop l2. Moisture supply for the pad is indicated di grammatically by thewater spray I4, which is merely an arrangement for maintainin moist.

,tured to be sold perfectly dry, in cut sheets or stable under ordinarystoring and handling conditions. It is economical,

ing-fairly frequently and to spread new and fresh has been accepted aspart of the practice in this art.

The present invention is directed to solvin the problem of maintainingwater balance, 'now encountered in the art of printing by theferrogelatin process. Briefly, it may be characterized as wetting thebackof the printing plate, the moisture passing through the plate to theprintwet strength or saturatin paper.

- ,The paper functions as a The printing-plate In is an effected sheetof upper surface with gelatin. It can be manufacrolls, and is perfectlyand satisfactory to use.

easy to make, and easy and prefer- Theprinting plate hereof may be ablyis free of glycerine since it is not required to be hygroscopic, for itis not intended that the water balance for the gelatin surface bemaintainedby absorption of moisture from the air, but rather it isintendedthat the water balance be maintained by the transfer of moisturefrom the felt pad H, through the printing plate itself, I

to the printing surface. Thus the printing plate hereof is far lessaffected by. storing and handling conditions than plates containinglycerine in 'which water balance is maintained by the hygroscopicaction of the glycerine.

moisture transfer medium, to transfer moisture from the source,

namely the felt I pad the pad l l continuously.

coated on its.

II. to the gelatin surface,

and thus is required to be of a character that retains its strengthduring the moisture transfer. For this purpose, it might well be anywell known wet strength or saturating or absorbent paper. One paper thathas been found suitable is a paper obtained from the Brown PaperCompany, and known as fNo. '20l Aqualized Kraft." saturating Tissue,such as is sold by the Process Manufacturing Company, of Chicago,Illinois, has been found satisfactory. Vegetable parchment papers havealso been found satisfactory.

The paper need not have any capacity for storing moisture, since onlyits moisture transfer characteristic is relied upon to maintain thewater balance.

With gelatin, the usual plasticizers, hardeners, fillers, etc., all wellknown to the art, may be and preferably should be incorporated withinthe coating.

Though the gelatin coating is to be utilized in the ferrogelatinprocess, it need not be originally formed with the secondary chemical ofthat process, ferrosulphate or its equivalent. Instead, the gelatin maybe plain, but it will be sensitized or activated, just before it isengaged by the original, by dampening or moistening it with aferrosulphate solution. This may be done from the front or the back.Thereafter, the moisture balance for printing is maintained by thetransfer of moisture through the printing plate from the back, where theprinting plate is in contact with the wet felt pad. While it iscontemplated to apply the sensitizing solution from the front, it is, ofcourse, obvious that if desirable, it also might be applied from theback, but except in so far as the sensitizing is e. moistening step,this is not particularly important. While felt has been used and foundsatisfactory for pad ii, it is apparent that from the point of view ofmoistening the back of the printing plate, other forms of supports orpads for the plate it might well be used. For example, instead of a padof felt, the support it might well be porous plaster block, or a poroussynthetic block of any suitable character.

It has been found that maintaining the water balance for printing in themanner here described, by transfer through the printing plate from theback to the printing surface, is better than any presently known methodof maintaining water balance. With gelatin, moisture transferred to itthrough the paper is molecularly and even y absorbed by the gelatin,with no excess. and withness of distribution of the moisture occurs,with the result that the ink spreads, or emulslfies, and

the unaffected or unhardened or background portions of the gelatin swellunevenly around the chemically afiected or hardened or image portions ofthe gelatin to cause hills and valleys on that coating, and reproductionis not so satisfactory. Where there is evenness of distribution of themoisture, either no swelling of the unhardened gelatin background takesplace, or else the swelling of the unaffected or unhardened gelatin isaccompanied by a similar swelling ofthe chemically affected or hardenedgelatin image. Where the moisture passes through the paper, enteringfrom the back, as in the present case, the undesirable conditions andfactors are eliminated, and, with less difllculty, better reproductionis obtained.

If desired, the paper may be supplied with wetting agents, having atendency to increase the absorption and transfer qualities of the paper.These agents might 'be applied to the paper during the manufacture ofthe paper, or might be incorporated in the wetting solution.

The present invention is of particular value where gelatin coatings arethin, as for example, where the gelatin is in the form of a thincoating, applied to paper, and stored dry. With such plates, the wettingand maintaining of water balance is a far more delicate operation, andyet is far more important, than under conditions where thick gelatincoatings, frequently renewed, are used in humidity controlled rooms.

Now having described the art of printing herein disclosed, referenceshould be had to the claim v which foliows:

We claim:

In the art of printing with moisture repelled, greasy, printers" inkwith a non-hygroscopic gelatin surfaced thin water absorbent wetstrength paper printing plate having a superficial printing image ofhardened gelatin on and surrounded by an unhardened ferrogelatinbackgrounithe image having been produced on the background by surfacecontact thereof with an original image containing a primary chemicalwhich reacts superficially with the ferrogelatin background to hardenthe engaged portions thereof to form the superficial hardened image, sothat there is unhardened gelatin underlying the image area as well assurrounding it, the step of feeding moisture to the plate from the backthereof, so that the moisture passes through the plate to the printingsurface thereof, thus maintaining the water balance therefor, and also.maintaining a constant minimum differential of level of the image andnon-image areas.

